In a distributed antenna system network a number of antennas are distributed geographically to cover a geographic area (a cell), each antenna covering a particular part thereof. The distributed antenna system is typically deployed in an indoor environment and uses a rather low transmission power. The antennas, also denoted remote radio heads in the following, are all connected by means of a respective cable to a radio unit, which thus receives signals from and transmits signals to the various remote radio heads. The single radio unit (or radio base station) may thus provide coverage e.g. in different parts of a building, each part having a properly placed remote radio head. A communication device can then move between the coverage of the different remote radio heads while staying within the same cell.
A communication device located at a downlink (DL, the direction from base stations to the communication device) cell border between the coverage of the distributed antenna system network and the coverage of a high transmission power network node (e.g. base station of a macro cell) will be at the point where it receives signaling from both cells with approximately the same strength. At this cell border, there may be a large difference between the DL transmission power sent from the remote radio head on the one hand and the DL transmission power sent from the base station of the macro cell on the other hand. The communication device, receiving signaling from both cells with approximately same strength, will then be much closer to the remote radio head than to the base station of the macro cell.
At this downlink cell border, the uplink (UL, the direction from the communication device to the base stations) path loss is much lower to the remote radio head than to the base station of the macro cell. This means that the radio unit cell will be dominating the power control of the communication device. This leads to the UL power being regulated down to a level that is suitable for the remote radio unit cell, but that is much too low for the macro cell.
This UL/DL imbalance leads to problems e.g. in view of soft handover, and also e.g. if the macro cell provides a high-speed downlink packet access (HSDPA) service to the communication device, since the macro cell will, in this scenario, have difficulties receiving a high-speed dedicated physical control channel (HS-DPCCH), which is only decoded in the serving cell (i.e. in the macro cell providing the DL HS service). The HSDPA throughput for the communication device will thus suffer. Still another problem is the ability of the communication devices to perform a successful random access.